This invention relates generally to sorbing materials and more particularly to fibrous sorbing materials.
Many modern research efforts, effulent waters from nuclear reactors, and the discovery of injurious effects of trace impurities in drinking water make the elimination of minute quantities of impurities in water a necessity. For example, Radium-226, a naturally occurring radioactive daughter of uranium-238, presents a potential health hazard when dissolved in ground waters. The body metabolizes radium and calcium similarly; thus, if radium is available to the bloodstream, it will concentrate in the bones. Radioactive decay of radium-226 within the bones exposes the skeleton to highly ionizing, short-range alpha particles as well as more penetrating beta and gamma radiation from radium daughters. The most immediate effect of this radiation is to increase the chances of developing osteosarcoma and other cancers. Although the exact relationship between low level radium exposure and cancer risk is not known, there is probably no safe level of human exposure to radium. The drinking water standards published by the U.S. Public Health Service recommend a level not to exceed 3 picocuries (pCi) per liter (6.66 disintegrations per minute (dpm) per liter).
Removal of trace constituents from large volumes of liquids requires an extremely efficient means. The techniques generally used may be classified as ion exchange, precipitation, and solvent extraction.
Conventional ion exchange techniques employ an activated particulate through which the liquid is slowly percolated. Depending on the conditions various components may be removed; however, the particulate materials have a low surface area per unit mass and must be tightly packed to be effective. The materials do not generally allow removal to be conducted at high flow rates. They are also generally expensive and may suffer radiation damage. Another ion exchange technique is the use of an activeated fiber, e.g., acrylic fiber impregnated with iron hydroxide. Other examples of activated fibers are phosphorus cotton fibers and ferric oxide cotton fibers. These fibers have been shown to be inefficient for radium retrieval from both fresh and sea water.
Precipitation involves the chemical precipitation of either the constituent of interest or of a scavenger which removes the component of interest. Precipitation cannot be done as a flow process without a continuous flow centrifuge or filtration apparatus. These techniques are objectionable for their inconvenience, cost, and inefficiency.
Solvent extraction is based on the affinity of various components for organic liquids or solutions which are water insoluble and immiscible. Under controlled conditions, components of interest may be extracted into the organic phase which may then be separated from the aqueous phase by flotation or centrifugation. This process is usually not as efficient in terms of the percent removal as the ion exchange or precipitation processes.
Methods usually used to specifically purify drinking water parallel the previously discussed techniques. The major difference is their lower efficiency and often these techniques are designed to eliminate only one type of impurity, e.g., mercury or germs. As a result, these techniques are being proven to be inadequate to safeguard public health by findings of medical research that even the smallest amounts of certain contaminants in drinking water have an adverse effect on the health of humans. Further these techniques are objectionable from one or more other considerations, such as cost, speed, or durability.
It is therefore an object of this invention to provide a means and method for purifying liquids.
Another object of this invention is to provide a means and method for purifying water.
Another object is to provide an efficient means and method for removing trace elements from water.
Another object is to provide a simple, cheap, and versatile means and method for removing trace elements and other impurities from water.
And another object is to provide a filter for water which is durable and require infrequent regeneration.
A further object is to provide a material removing means which can process large volumes of water quickly and continuously.
A still further object is to provide a filtering material which can be easily incorporated in a filter which can be added to an effulent water conduit of a nuclear reactor or a factory.
And a still further object of this invention is to provide a filtering material which can be easily incorporated in samples to be towed by a ship.
Also an object of the invention is to provide a method and means for purifying water which does not require any special water preparation or added filtering aid.
And a further object is to provide a material removing means which has little back up pressure and no channeling.
And still another object is to provide methods of placing a manganese oxide coating on acrylic fibers.
These and other objects are achieved through coating acrylic fibers with manganese oxides so strongly and heavily and without serious damage to the fiber that the resulting materials can continuously remove metals and radioisotopes even from water in which the impurity concentration may be as low as 1 ppm.